1. Field of the Invention
The present invention relates to a high pressure drying apparatus and a high pressure drying method in which a high pressure fluid or a mixture of a high pressure fluid and a chemical agent as a processing fluid is supplied to substrates, to thereby dry the substrates under a high pressure. The present invention relates also to a substrate processing apparatus comprising such a high pressure drying apparatus. The substrates include a semiconductor wafer, a glass substrate for photomask, a glass substrate for liquid crystal display, a glass substrate for plasma display and an optical disk substrate
2. Description of the Related Art
While electronic components such as semiconductor devices are becoming increasingly finer these days at an accelerating rate, there are new problems arising because of this during processing of substrates. For example, a developing process, a rinsing process and a drying process are performed in this order to form very fine patterns by means of patterning of a resist which is applied on a substrate. During an alkaline developing process for development of the resist applied on the substrate, an alkaline solution is used for removal of an unwanted resist. During rinsing, a rinse liquid such as pure water is used to remove the alkaline solution (to stop developing). During drying, the substrate is rotated to thereby make centrifugal force act upon the rinse liquid, the rinse liquid remaining on the substrate is accordingly removed, and the substrate is dried (spin drying). Of these processes, during the drying process, the interface between the rinse liquid and gas appears on the substrate as drying proceeds. If the interface appears at a gap between very fine patterns of a semiconductor device, the surface tension of the rinse liquid pulls the very fine patterns toward each other and collapses the very fine patterns, which is a problem.
It is also considered that the collapse of the very fine patterns is attributed to the flow resistance created at the time of spin drainage of the rinse liquid, the applied pressure developed at the time of ejection of the rinse liquid out from the very fine patterns, the air resistance and the centrifugal force due to the high-speed rotations beyond 3000 rpm, etc.
Proposed as a solution of this problem is supercritical drying during which a substrate is held inside a pressure container, a supercritical fluid (hereinafter referred to as xe2x80x9cSCFxe2x80x9d) which has low viscosity, high diffusivity and no surface tension is introduced into the pressure container, and the substrate is subjected to supercritical drying. One such a conventional technique is a supercritical drying apparatus described in Japanese Patent Application Laid-Open Gazette No. 2000-223467. This supercritical drying apparatus is capable of holding a developed and rinsed substrate inside a reaction chamber. A pump unit is activated with a substrate held, a constant amount of liquefied carbon dioxide is pumped under pressure into the reaction chamber from a cylinder, the pressure of carbon dioxide inside the reaction chamber is automatically controlled by means of a pressure control valve, the pressure of carbon dioxide inside the reaction chamber accordingly becomes 7.38 through 8 MPa, and carbon dioxide inside the reaction chamber consequently becomes a supercritical fluid. Supercritical carbon dioxide is thereafter released from the reaction chamber and the pressure inside the reaction chamber is reduced, whereby the substrate is dried.
By the way, the supercritical drying apparatus described above is a drying apparatus of the single wafer type which performs only drying. Therefore, after a different developing apparatus which is separate from the supercritical drying apparatus develops and rinses one substrate, this substrate is fed into the supercritical drying apparatus by a transportation apparatus and dried. Thus, a developing apparatus, a transportation apparatus and a supercritical drying apparatus are disposed within a conventional substrate processing apparatus, and substrates are processed one by one in each one of the developing apparatus and the supercritical drying apparatus. In short, the developing apparatus and the supercritical drying apparatus are both of the single wafer type.
As for comparison of a processing time per production lot between the developing apparatus and the supercritical drying apparatus, the processing time of the supercritical drying apparatus is longer than that of the developing apparatus. It is a reason that the supercritical drying apparatus requires an operation of increasing the pressure inside a reaction chamber and generating a supercritical fluid for the purpose of supercritical drying and thereafter releasing the supercritical fluid and decreasing the pressure inside the reaction chamber. Hence, the supercritical drying step becomes a causes of the throughput-determining of the substrate processing apparatus as a whole.
A major object of the present invention is to provide a high pressure drying apparatus, a high pressure drying method and a substrate processing apparatus with which it is possible to perform high pressure drying on substrates at an excellent throughput.
To achieve the object above, a high pressure drying apparatus according to the present invention comprises: a pressure container whose inside is a processing chamber; substrate housing means which is capable of housing a plurality of substrates inside the processing chamber; atmosphere creating means which provides the processing chamber with an anti-drying liquid for prevention of drying of surfaces of substrates or a vapor of the anti-drying liquid, to thereby create an anti-drying atmosphere; atmosphere removing means which removes the anti-drying atmosphere from the processing chamber; and processing fluid introducing means which introduces into the processing chamber a high pressure fluid or a mixture of a high pressure fluid and a chemical agent as a processing fluid, wherein after more than one substrate among substrates transported to the processing chamber are housed in the substrate housing means and made on stand-by in the anti-drying atmosphere, the more than one substrate housed in the substrate housing means are subjected all at once to high pressure drying.
To achieve the object above, a high pressure drying method according to the present invention comprises: a first step of supplying an anti-drying liquid, which prevents drying of surfaces of substrates, or a vapor of the anti-drying liquid to a processing chamber of a pressure container and creating an anti-drying atmosphere inside the processing chamber; a second step of receiving substrates transported to the processing chamber and making the substrates on stand-by in the anti-drying atmosphere; and a third step of removing the anti-drying atmosphere from the processing chamber after repeating the second step for a plurality of times, introducing a high pressure fluid or a mixture of a high pressure fluid and a chemical agent into the processing chamber as a processing fluid, and subjecting the substrates all at once to high pressure drying.
According to the present invention using such a structure (the high pressure drying apparatus and the high pressure drying method), more than one substrate among substrates transported to the processing chamber, as they are housed in the substrate housing means, are dried all at once under a high pressure, and therefore, the throughput dramatically improves as compared to a conventional apparatus which performs single wafer processing.
Batch type high pressure drying of drying more than one substrate all at once requires to consider the following points. Prior to high pressure drying of more than one substrate all at once, if substrates which have been already housed dry up naturally while transported substrates are housed one by one in the substrate housing means, very fine patterns pull each other and collapse because of the surface tension of the anti-drying liquid, and execution of high pressure drying accordingly becomes meaningless. On the contrary, the anti-drying atmosphere is created within the processing chamber in advance and each substrate is kept on stand-by in the anti-drying atmosphere before subjected to high pressure drying according to the present invention. Hence, air drying of the substrates which are on stand-by is prevented.
In addition, since high pressure drying is performed after each substrate is made on stand-by inside the same processing chamber without air-drying the substrates according to the present invention, it is possible to effectively reduce the footprint and a cost. The reason is as follows. An approach to merely prevent air drying of substrates before high pressure drying may be to keep the substrates on stand-by within a stand-by bath which holds a liquid up until high pressure drying, transport more than one substrate all at once from the stand-by bath to a processing chamber, and perform high pressure drying. However, this approach demands to separately dispose the stand-by bath and a transporting mechanism, which further necessitates an extra area to install these additional structures and increases a cost on the apparatus by an additional cost for the additional structures. On the contrary, since the present invention does not need such additional structures at all, the present invention is advantageous in terms of foot print and apparatus cost.
A high pressure fluid used in the present invention is preferably carbon dioxide because of the safety, the price, the easiness to be transformed into a supercritical state, etc. Water, ammonia, dinitrogen monoxide, ethanol and the like may be used, other than carbon dioxide. A high pressure fluid is used because of its high diffusion coefficient and its capability of dispersing a dissolved contaminant in a medium. As for use of a supercritical fluid in particular, the reason is that the supercritical fluid exhibits a property between gas and liquid and can further penetrate even between very fine patterns but yet does not exhibit surface tension. In addition, the density of a high pressure fluid is close to that of liquid, and a high pressure fluid can contain a far greater amount of an additive (chemical agent) than gas.
Further, a high pressure fluid referred to in the present invention is a fluid whose pressure is 1 MPa or higher. A preferable high pressure fluid is a fluid whose properties include high density, high solubility, low viscosity and high diffusivity, and a further preferable high pressure fluid is a fluid which is in a supercritical condition or a subcritical condition. Carbon dioxide may be heated to 31xc2x0 C. and pressurized to 7.1 MPa or higher so that carbon dioxide will become a supercritical fluid. For a drying step in particular, a subcritical fluid (high pressure fluid) or a supercritical fluid at 5 through 30 MPa is preferably used, and it is further preferable to process with these at 7.1 through 20 MPa.
When the component of the anti-drying liquid is not compatible with a high pressure fluid, instead of using a high pressure fluid alone as a processing fluid as described above, a compatibilizer which can serve as an auxiliary which dissolves or uniformly diffuses the component of the anti-drying liquid in carbon dioxide is used as a chemical agent. In other words, it is preferable to use a mixture of supercritical carbon dioxide and a chemical agent as a processing fluid.
The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawing. It is to be expressly understood, however, that the drawing is for purpose of illustration only and is not intended as a definition of the limits of the invention.